SATGuard: SAT-driven Countermeasures for Protecting Approximate Circuits from Hardware Trojan
Vishesh Mishra, Dipesh, Sparsh Mittal, Urbi Chatterjee · ACM Transactions on Embedded Computing Systems · 2025
Approximate arithmetic circuits have gained prominence in modern computing systems due to their ability to trade accuracy for improved performance and energy efficiency. However, their susceptibility to stealthy Trojan attacks poses a significant security concern. This work analyzes Trojan attacks on approximate circuits, focusing specifically on approximate adders and multipliers. We propose SATGuard, a boolean satisfiability (SAT)-based methodology to identify Trojan activating inputs (TAIs) for all approximate adder and multiplier families. We also claim that TAIs for approximate circuits are analogous to test input patterns for accurate circuits. Subsequently, we propose design-specific countermeasures to safeguard approximate circuits. The proposed countermeasures nullify the Hardware Trojan Horse (HTH)-based accuracy degradation, thus upholding the application-level accuracy requirements. We conduct experiments where potential Trojans are implanted into various approximate adders and multipliers. We evaluate their impact on the error metrics and the quality of results in real-world applications such as image processing and deep neural networks (DNNs). Our findings demonstrate that the proposed methodology successfully reverses the HTH-based accuracy degradation by 99.4%, and 99.8% in approximate adders and multipliers, respectively. This improvement is achieved with an average area overhead of 5.3% and a power-delay-product overhead of 7.6% in approximate adders and 1.7% and 1.9% in multipliers, respectively.